05-30 03:15:54.127 647-664/com.jdk8.minifacebookloginapp.app E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:299)
at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
at java.util.concurrent.FutureTask.run(FutureTask.java:137)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
at java.lang.Thread.run(Thread.java:856)
Caused by: java.lang.NullPointerException
at java.util.concurrent.ConcurrentHashMap.containsKey(ConcurrentHashMap.java:781)
at com.facebook.internal.Utility.queryAppSettings(Utility.java:372)
at com.facebook.widget.LoginButton$1.doInBackground(LoginButton.java:676)
at com.facebook.widget.LoginButton$1.doInBackground(LoginButton.java:673)
at android.os.AsyncTask$2.call(AsyncTask.java:287)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
at java.util.concurrent.FutureTask.run(FutureTask.java:137)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
at java.lang.Thread.run(Thread.java:856)

The error last two triggering lines are from the facebook sdk (com.facebook.internal) and your java.util package neither of which are from your code.

To fix this, you need to finish the setup in the facebook's getting started tutorial for android where you register your app after generating an android key hash. After you've done that, open your AndroidManifest.xml and add the meta-data line